This invention relates to a process for obtaining high levels of acoustic attenuation in a tungsten-polyvinyl chloride composite and to an improved high frequency ultrasonic transducer.
Tungsten-PVC composites are commonly used as backings in transducer assemblies. Ideally, all of the acoustic energy entering the backing should be dissipated there. Often this is not the case and the acoustic energy reflected from the interior of the backing returns to the element giving rise to spurious signals. The effective sensitivity of the transducer is limited by these unwanted signals.
Tungsten-PVC composites have been prepared containing relatively large tungsten particles (50 micron diameter) which act as scattering centers, thereby increasing the attenuation in the composite. The acoustic waves are reflected by the large particles and have a longer path length. This system, with 30-50 percent large particles and the balance of the tunsten as small particles, is good at low ultrasonic frequencies but is not very effective at frequencies greater than about 4.5 MHz. At the higher frequencies the large particles reflect increasing amounts of acoustic energy back into the element, and as a result the noise level increases.